Neutron Diffraction Study on the Antiferromagnetic Insulating Ground State of β-Na0.33V2O5

Abstract

The magnetic structure of the antiferromagnetically ordered state of a quasi-one-dimensional conductor β-Na 0.33 V 2 O 5 below T N =24 K was examined by neutron diffraction. The presence of magnetic Bragg reflections at ( h , k ±1/6,0), h + k =odd below T N indicates that the amplitudes of the magnetic moments at the V sites in three types of V–O chains are modulated with a period of 3 b along the chain direction (∥ b ). On the other hand, it was confirmed that the lattice modulation along the b direction occurs at ∼244 K and at ∼131 K with a period of 2 b and 6 b , respectively. Although the latter structural transition had been attributed to a “charge ordering” transition, which would result in a charge disproportionation in the V 3 d orbitals with a period of 6 b , the 3 b periodicity in the amplitude of magnetic moments strongly suggests that the charge disproportionation occurs with a period of 3 b , not 6 b . The 6 b lattice modulation developing below 131 K is therefore attributed to an instability...